The traditional Fourdrinier papermaking process substantially includes three subsequent steps, carried out in corresponding sections of the papermaking machine: forming section, pressing section, drying section.
In the forming section, an aqueous pulp of cellulose fibers (and possibly other components) is arranged on a so-called forming fabric, loop-closed and supported by rollers. The removing of water from the pulp through the forming fabric leads to the gradual formation of a wet paper material web with still relatively high water content. Further removing of water takes place in the pressing section, in which the paper material is pressed passing through one or more pairs of rollers. The paper material is then sent to the drying section for removing the remaining moisture. The paper thus formed is ready for the subsequent steps of finishing and packaging.
Hereinafter, as customary in the papermaking industry, the terms “machine direction” (abbreviated “MD”) and “cross machine direction” (abbreviated “CMD”) are used to indicate a direction aligned with the feeding direction of the forming fabric in the papermaking machine and a direction parallel to the surface of the fabric and crosswise (orthogonal) to the feeding direction, respectively. The direction or orientation of the warp and weft yarns of the forming fabric are also indicated with reference to machine direction and cross machine direction.
Furthermore, again as customary in the industry, the surface of the forming fabric in contact with the cellulose pulp (i.e. with the paper material being formed) is the top surface of the fabric and the opposite side facing the machine is the bottom surface. This reference will be adopted also to describe the vertical spatial arrangement of the yarns in the forming fabric.
Some features of the papermaking fabrics are particularly important, such as the supporting capacity and the filtering capacity, especially in the forming section.
Furthermore, papermaking fabrics must have excellent stability also when moved at high speed, high permeability for reducing the amount of water withheld in the pulp when it is transferred to the pressing section and a low energy consumption for moving them.
Although various types of papermaking fabrics, are known, in particular for use in the forming section, there still appears to be margin for improvement in the industry, e.g. in terms of mechanical strength, stability, durability, draining capacity and quality of the formed paper.